In a current communications system, a radio frequency unit is an important component, and a power amplifier (PA) is an important radio frequency device thereof, and has a function of amplifying an input signal. However, the PA may bring in nonlinear distortion. That is, an output signal and an input signal are in a nonlinear amplification relationship. In addition, if the input signal is a broadband signal, the PA may have a memory effect. That is, the output signal is not only correlated with an input signal that is at a current time point, but also correlated with input signals that are at some earlier time points. The nonlinear distortion and the memory effect may cause impact in two aspects on a signal output by the PA: One is an increase of in-band distortion of the signal, which causes that a receive end cannot correctly receive the signal; and the other is an increase of out-of-band power leakage of the signal, which causes interference on a communications system of an adjacent band.
A method for reducing a nonlinear distortion effect of a PA in the prior art is to use digital pre-distortion (DPD). The DPD is a very effective method for reducing nonlinear distortion of a signal output by the PA, and is widely used in the industry. Specifically, a DPD module is located before the PA. A nonlinear component generated by an input digital intermediate frequency signal according to a pre-distortion model offsets a nonlinear component generated by the PA, thereby fulfilling a purpose of improving output linearity of the PA.
However, in a scenario in which a multiband signal is amplified, the existing DPD technology cannot effectively eliminate out-of-band intermodulation distortion.